Breaking the 3 GHz Barrier with the Pentium 4 Processor

Breaking the 3 GHz Barrier with the Pentium 4 Processor

The newest Pentium 4 processor is the first desktop processor
to break the 3 GHz barrier. The first models, S-spec models SL6S5 and SL6SM,
run at 3.06 GHz, and future versions will run at even faster clock speeds.

When you examine the basic specifications of the new 3.06 GHz
Pentium 4, at first glance theres not much difference between it and other
recent P4 processors, other than the clock speed. 512KB Level 2 cache and 533
MHz bus speeds have been standard on Pentium 4 processors for quite some time
(see Chapter 3 of Upgrading and Repairing PCs, 14th Edition
for complete details). However, the 3.06 GHz P4 processor has a feature that
has never been available to the user in any previous Pentium 4 processor: Hyper-Threading
(HT) technology.

What Is Hyper-Threading Technology?

The new 3.06GHz and higher Pentium 4 processors support Hyper-Threading,
which is a method for turning a single physical processor into two virtual processors,
with each virtual processor handling different threads (series of tasks).

In most cases the additional costs of a second physical processor
and the limited number of operating systems which support multiple processors
have discouraged widespread adoption of multiprocessor systems. HT technology
is designed to bring many of the benefits of these systems to single-processor
systems. Intel originally introduced HT technology in its 2+ GHz line of Xeon
processors for servers; HT technology enables multi-processor servers to act
as if they had twice as many processors installed.

However, HT technology benefits arent limited to server tasks.
Hyper-Threading technology enables a single HT-enabled processor to handle two
processes, or threads, at the same time. Internally, a HT-enabled processor
has two sets of general-purpose registers, control registers, and other architecture
components, but both logical processors share the same cache, execution units,
and buses. The additional components used by HT technology have been incorporated
into the P4 core since the 478-pin Northwood design was introduced, but they
were never enabled until the introduction of the 3.06 GHz processors. This delay
has enabled Intel to develop chipsets that support faster memory (333 MHz DDR
SDRAM and 1066 MHz RDRAM) to better take advantage of virtual multiprocessing
and to work out any bugs in the design.

Although the sharing of some processor components means that
the overall speed of an HT-enabled system isnt as high as a true dual-processor
system would be, Hyper-Threading is designed to improve CPU utilization by as
much as 40%, particularly when the processor threads are not trying to use the
same resource. Benchmarks are showing that the normal gain in performance is
about 20%, meaning that merely turning on HT technology can improve overall
processor performance by that amount on average. This is like turning a 3.06
GHz processor into a 3.7 GHz processor!

What You Need to Use Hyper-Threading Technology

To be able to activate and utilize HT technology, you will
need the following:

Pentium 4 3.06 GHz or higher

Motherboard Chipset that supports HT technology

Motherboard BIOS that supports HT technology (and has it
enabled)

An operating system that includes support for HT technology.

All 3.06 GHz and faster Pentium 4 processors support HT technology.
Although older Northwood core processors also have the HT circuitry, it was
not fully tested and there is no way to activate it.

Hyper-Treading Technology-Compatible Chipsets

Initially, the only chipsets which can support HT technology-enabled
P4 processors include the following members of Intels 845 family:

845G (B-1 or higher steppings only)

845GE

845GV

845E

845PE

Basically all 845-series chipsets with 533 MHz FSB support
will support HT-enabled processors, except that the 845G chipset supports HT
only in the B-1 or higher steppings of the chipset. To learn more about these
chipsets, read my article, The Intel 845 Chipset Family.

Third-party chipset vendors such as SiS and VIA are expected
to support HT technology at some point; check their Web sites for announcements.

BIOS Support

Even if your motherboard uses a chipset that supports HT technology,
you might need a BIOS update. A system BIOS that properly supports HT technology
provides a way to enable or disable Hyper-Threading. If your operating system
doesnt support HT technology, or if your mix of applications run more slowly
when HT technology is enabled, you should disable it. When HT technology is
enabled, the BIOS will report two virtual processors to the operating system.

To determine if your BIOS can support HT technology, restart
your computer, run the BIOS setup program, and look for a setup menu option
such as Hyper-Threading technology or HT technology. If you dont see this option,
contact your motherboard or system vendor for a BIOS upgrade.

Operating System Support

According to Microsoft, the only current Windows operating
systems which completely support HT technology are Windows XP Professional and
Windows XP Home Edition in their Service Pack 1 and later updates. Its not
surprising that XP Professional supports HT technology, since its been designed
for multi-processor support from the start. However, support for Windows XP
Home Edition is a welcome benefit for users of this operating system, which
cant support multiple physical processors.

Windows 2000 Professional can run with HT technology enabled
(single-processor systems only), but Windows 2000 Server could have problems
using HT technology if the system BIOS doesnt start the logical processors
inside each physical processor in the correct order. If you use Windows 2000
Server and plan to upgrade to systems using HT technology, you should download
the Windows Support for Hyper-Threading technology white paper from http://www.microsoft.com/hwdev/platform/proc/ht-windows.asp.

Linux releases based on Linux kernel version 2.4.18 and above
are also compatible with HT technology-enabled processors.

Building Your Own HT technology-Enabled System

If you buy a system that already includes an HT technology-enabled
P4 processor and Windows XP, chances are the only concern you have is how to
access the system BIOS to enable or disable this feature. However, if you prefer
to build or upgrade your own systems, you should follow the instructions provided
by Intel in its integration overview for P4 processors with HT technology: http://support.intel.com/support/processors/pentium4/pentium4_ht.htm

The overview explains how to configure your system for proper
use of HT technology, and how to use the Windows XP Task Manager and Device
Manager to verify proper operation.

Conclusion

The introduction of HT technology in the 3.06 GHz and faster
Pentium 4 processors enables these processors to take greater advantage of their
high clock speed to provide better performance. While the full benefit of HT
technology wont be apparent until applications are rewritten to be fully HT
technology-aware, many existing programs will run significantly faster when
HT technology is enabled. Since you can enable or disable HT technology as needed
for a particular boot cycle, you can experiment to determine which setting is
best for the work you do.